Selectively Storing Reformate

ABSTRACT

Systems and methods are provided for selectively storing gaseous reformate output by a fuel reformer for fueling an engine. Carbon monoxide produced by a fuel reformer may be continuously combusted in the engine and/or engine exhaust rather than being stored. In one example, reformate components produced by a fuel reformer, e.g., H2 and CH4, may be stored and buffered for use by an engine.

FIELD

The present description relates to systems and methods for operating anengine with a fuel reformer.

BACKGROUND AND SUMMARY

Fuel reformers can be used to convert alcohol fuels into gaseous fuels(reformates) to fuel an engine. For example, an ethanol reformer canreform ethanol into a reformate gas comprising hydrogen (H₂), carbonmonoxide (CO), and methane (CH₄) for combustion in an engine. The fuelreformer reaction may be driven by recovered exhaust heat from theengine and gaseous reformate output by the reformer may be stored, e.g.,as a compressed or adsorbed gas, for use by the engine.

The inventors herein have recognized that since reformate output by afuel reformer may include CO, storage of reformate may be degraded dueto the presence of CO with the remaining gasses.

In one example approach, in order to at least partially address theabove issues, a method for operating an engine is provided. The methodcomprises: reforming a fuel into a gaseous fuel comprising H₂, CO, andCH₄; and selectively storing at least one or both of H₂ and CH₄. Forexample, CO produced by the reformer may be combusted in the engineand/or engine exhaust rather than being stored.

In this way, reformate components produced by a fuel reformer, e.g., H₂and CH₄, may be stored and buffered for use by an engine. Such bufferingenables more or less of the H₂ and CH₄ to be delivered to the enginecommensurate with operating conditions, without also requiring storageof CO with the H₂ and CH₄. Rather, the CO may be delivered to the enginewithout buffering, as its effect in controlling engine operation, suchas knock mitigation, etc., is less than that of the remaining reformategases (H₂ and CH₄).

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of an engine with a fuel reformer.

FIG. 2 shows an example method for selectively storing gaseous reformateoutput by a fuel reformer.

FIG. 3 shows an example method for storing non-CO reformate output anddelivering non-CO reformer output to the engine.

FIG. 4 shows an example method for purging CO from a CO trap at anengine shutdown.

DETAILED DESCRIPTION

The following description relates to systems and methods for operatingan engine with a fuel reformer, a schematic example of which is shown inFIG. 1. Fuel reformers can be used to convert alcohol fuels into gaseousfuels (reformates) to fuel an engine. For example, an ethanol reformercan reform ethanol into a reformate gas comprising hydrogen (H₂), carbonmonoxide (CO), and methane (CH₄) for combustion in an engine. Use ofgaseous reformate in an engine may assist in highly dilute operation,engine cold starts and engine knock reduction, e.g., during high loadengine operating conditions.

The fuel reformer reaction may be driven by recovered exhaust heat fromthe engine and gaseous reformate output by the reformer may be stored,e.g., as a compressed or adsorbed gas, for use by the engine.

When a fuel is reformed into a gaseous fuel, the gaseous fuel may beselectively stored onboard the engine or delivered to the engine toassist in cold starts and/or knock suppression, for example as shown inFIG. 2. For example, CO may be separated from the gaseous fuel andcontinuously combusted in the engine or exhaust. In this way, reformatecomponents produced by a fuel reformer, e.g., H₂ and CH₄, may be safelystored for use by an engine.

Turning now to FIG. 1, a schematic diagram of one cylinder ofmulti-cylinder engine 10, which may be included in a propulsion systemof an automobile, is shown. Engine 10 may be controlled at leastpartially by a control system including controller 12 and by input froma vehicle operator 132 via an input device 130. In this example, inputdevice 130 includes an accelerator pedal and a pedal position sensor 134for generating a proportional pedal position signal PP. Combustionchamber (i.e., cylinder) 30 of engine 10 may include combustion chamberwalls 32 with piston 36 positioned therein. Piston 36 may be coupled tocrankshaft 40 so that reciprocating motion of the piston is translatedinto rotational motion of the crankshaft. Crankshaft 40 may be coupledto at least one drive wheel of a vehicle via an intermediatetransmission system. Further, a starter motor may be coupled tocrankshaft 40 via a flywheel to enable a starting operation of engine10.

Combustion chamber 30 may receive intake air from intake manifold 44 viaintake passage 42 and may exhaust combustion gases via exhaust passage48. Intake manifold 44 and exhaust passage 48 can selectivelycommunicate with combustion chamber 30 via respective intake valve 52and exhaust valve 54. In some examples, combustion chamber 30 mayinclude two or more intake valves and/or two or more exhaust valves.Each intake and exhaust valve may be operated by an intake cam 51 and anexhaust cam 53. Alternatively, one or more of the intake and exhaustvalves may be operated by an electromechanically controlled valve coiland armature assembly. The position of intake cam 51 may be determinedby intake cam sensor 55. The position of exhaust cam 53 may bedetermined by exhaust cam sensor 57.

Intake passage 42 may include a throttle 62 having a throttle plate 64.In this particular example, the position of throttle plate 64 may bevaried by controller 12 via a signal provided to an electric motor oractuator included with throttle 62, a configuration that is commonlyreferred to as electronic throttle control (ETC). In this manner,throttle 62 may be operated to vary the intake air provided tocombustion chamber 30 among other engine cylinders. The position ofthrottle plate 64 may be provided to controller 12 by throttle positionsignal TP from a throttle position sensor 58. Intake passage 42 mayinclude a mass air flow sensor 120 and a manifold air pressure sensor122 for providing respective signals MAF and MAP to controller 12.

A fuel injector 66 is shown coupled directly to combustion chamber 30for injecting fuel directly therein in proportion to the pulse width ofsignal FPW received from controller 12 via electronic driver 68. In thismanner, fuel injector 66 provides what is known as direct injection offuel into combustion chamber 30. The fuel injector may be mounted in theside of the combustion chamber or in the top of the combustion chamber,for example. In some embodiments, combustion chamber 30 mayalternatively or additionally include a fuel injector arranged in intakepassage 44 in a configuration that provides what is known as portinjection of fuel into the intake port upstream of combustion chamber30. Fuel may be delivered to fuel injector 66 by a fuel system includinga fuel tank 91, a fuel pump within fuel tank 91 (not shown), a fuel line90, and a fuel rail (not shown).

In some examples, a plurality of fuel tanks may be employed. Forexample, the plurality of fuel tanks may include an ethanol fuel tankand a gasoline fuel tank. Each of the plurality of fuel tanks mayinclude a fuel pump and various other components used to assist indelivery of fuel to the engine.

A fuel reformer 97 is shown coupled to exhaust passage 48. Fuel reformer97 is configured to reform fuel supplied by fuel tank 91 via fuel line14 into a gaseous fuel reformate. For example, when a fuel in fuel tank91 includes ethanol, fuel reformer 97 may be configured to reform thefuel into a gaseous fuel reformate comprising H₂, CO, and CH₄.

A valve 16 may be positioned in fuel line 14 to divert fuel deliveryeither to the reformer or to the engine. Additionally a fuel sensor 18may be disposed in the fuel line to determine the type of fuel used,e.g. following a refueling event. In some examples, a fuel evaporatormay be employed to vaporize the fuel supplied to the fuel reformer.Thus, for example, a fuel evaporator of vaporizer chamber may bedisposed in fuel line 14 or within the same unit as the fuel reformer.Fuel may be injected to the reformer by way of a pump 96 disposed infuel line 14. In some examples, high pressures may be generated in thegases passing through the reformer. Thus in some examples, pump 96 mayinclude a hydraulic pressure multiplier to assist in delivery of fuel tothe reformer at high pressures. As another example, fuel may be injectedinto the reformer during low pressure conditions. For example, fuel maybe injected into the reformer when the amount of gaseous fuel output bythe reformer is below a threshold value.

Fuel reformer 97 includes a catalyst 72. In some examples, catalyst 72may include copper at a surface of a thermally conductive metalsupporting structure, e.g., copper-plated Raney nickel. For example, acatalyst may be prepared by depositing copper onto a nickel spongesupporting structure with high surface area.

Reformer 97 may use exhaust heat to drive an endothermic dehydrogenationof ethanol as it passes through the catalyst to promote reformation ofethanol into a gaseous reformate fuel comprising H₂, CO, and CH₄. Forexample, vaporized ethanol may pass over the catalyst surface while atan elevated temperature. Thus reformer 97 may be thermally coupled toexhaust passage 48. For example, catalyst 72 of reformer 97 may bethermally coupled to a portion of exhaust conduit 48. For example,gaseous reformate from ethanol may increase a fuel value of ethanol whendriven by a free source of heat, e.g., exhaust heat. Additionally,gaseous fuels may displace air in the intake manifold and thus lowerpumping work.

In some examples, fuel reformer 97 may include an electric heater 98 foradditional temperature control of the fuel reformer. Also, in someexamples, a reformer bypass conduit 20 may be disposed in the exhaustconduit in order to direct exhaust gas away from the reformer, e.g., tocontrol the temperature of the fuel reformer. Reformer bypass conduit 20may include a bypass valve 22 upstream of reformer 97 to control theamount of exhaust gas in thermal contact with reformer 97.

A CO trap 31 may be disposed in a reformer output fuel line 69 toseparate CO from gaseous fuel produced by reformer 97. In some examples,CO trap may employ a molecular sieve to separate CO from the reformategas output by the reformer. For example, a molecular sieve in CO trap 31may include aluminosilicate minerals, zeolites, or synthetic compoundsthat have open structures through which CH₄ and H₂ can diffuse.

In some examples, CO trap 31 may employ pressure swing adsorption toseparate CO from the reformer output. In pressure swing adsorption aplurality of adsorbent vessels may be included in CO trap 31. In thisway near-continuous separation of CO from the reformate output may beachieved.

CO separated from the reformer output by CO trap 31 may be delivered toan engine inlet and/or exhaust. Since CO is a fuel (e.g., a reductant),CO may at least partially assist in driving the engine throughcombustion. Separated CO may be delivered to the engine via a CO fuelline 33 and CO injector 35 disposed in intake manifold 44. In someexamples, separated CO may be injected directly to cylinder 30.Separated CO may be delivered to the engine exhaust via CO fuel line 37and CO injector 41 coupled to exhaust passage 48. Separated CO may bedirected to the engine and/or exhaust via a valve 43 disposed in a COoutlet in CO trap 31. For example, separated CO output by CO trap 31 maybe delivered to one or both of the engine and exhaust.

In some examples, valve 43 may be used during conditions when CO ispurged from CO trap 31. For example, if CO trap 31 includes a molecularsieve, then CO may be cyclically purged from the CO trap.

Non-CO gaseous components output by the reformer may be directed to areformate storage tank 93 via gaseous fuel line 45. Fuel line 45 mayinclude a valve 47 disposed therein to control delivery of gaseousreformate to reformate storage tank 93. In some examples, reformatestorage tank 93 may include an onboard CNG compressor 23 which may beused to compress and store at least a portion of non-CO gaseouscomponents.

Gaseous fuel produced by the reformer may be injected to intake manifold44 by way of a gaseous fuel injector 89. In other examples, gaseous fuelmay be directly injected into cylinder 30. Gaseous fuel may be suppliedto gaseous fuel injector 89 from a reformate storage tank 93. In someexamples, the pressure of the gaseous fuel output by the reformer may besufficient to assist in delivery of gaseous fuel to the reformatestorage tank 93, e.g., due to high temperatures in the reformer.However, in some examples a pump may be disposed in a reformate fuelline 69 to assist in pressurizing gaseous fuel output by the reformer. Acheck valve 82 disposed in reformate fuel line 69 limits flow of gaseousfuel from storage tank 93 to fuel reformer 97 when the gaseous reformateoutput by the reformer is at a lower pressure than storage tank 93. Insome examples, instead of or in addition to the reformate storage tank,gaseous fuel may be supplied to a fuel cell, e.g., in HEV vehicles.

If fuel reformer 97 is supplied with a blend of fuel including alcohol,a portion of the fuel that is not alcohol may not be reformed, thus maycondense. Thus, a heat exchanger 83 may be positioned in the reformatefuel line upstream of reformate storage tank 93 to assist in cooling ofthe gaseous reformate output by the reformer before it reaches thegaseous fuel injection system. In this way, condensate may be capturedin the reformate storage tank before reaching the gaseous fuel injectionsystem.

The reformate storage tank 93 may include a drain line 17 coupled tofuel line 90 to direct condensate from the reformate storage tank 93 tothe liquid injection line, e.g., fuel supply line 90. As such a checkvalve 13 may be positioned upstream of the intersection of the drainline 17 and fuel line 90 so as to prevent condensate from flowing backto the fuel tank. In some examples, condensate from the reformatestorage tank 93 may be returned to the fuel tank 91. Additionally, acondensate metering valve 19 may be disposed in drain line 17 to controlan amount of condensate delivered to the liquid injection line orreturned to fuel tank 91.

A fuel reformer system may include system components used by fuelreformer 97 for operation. For example, a fuel reformer system mayinclude fuel reformer 97, catalyst 72, fuel line 14, electric heater 98,a reformate fuel lines 69 and 71, reformate pump 96, reformate storagetank 93, drain line 17, and various sensors and other components coupledthereto.

In some examples, the fuel reformer system may include a water-gas shiftcatalyst to convert CO output by the reformer into CO₂ and H₂. Forexample, catalyst 72 may assist in a water-gas shift reaction to convertCO into CO₂ and H₂. In another example, a water-gas shift catalyst maybe disposed in reformate fuel line 69 in order to assist in a water-gasshift reaction. Examples of catalysts used to promote a water-gas shiftreaction include Fe₃O₄ (magnetite), or other transition metals andtransition metal oxides, and a Raney copper catalyst. In this way, COoutput by the reformer reaction may substantially be converted to CO₂and H₂.

Combustion chamber 30 or one or more other combustion chambers of engine10 may be operated in a compression ignition mode, with or without anignition spark. Distributorless ignition system 88 provides an ignitionspark to combustion chamber 30 via spark plug 92 in response tocontroller 12.

An exhaust gas sensor 126 is shown coupled to exhaust passage 48upstream of reformer 97. Sensor 126 may be any suitable sensor forproviding an indication of exhaust gas air/fuel ratio such as a linearoxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), atwo-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx, HC, or COsensor.

An exhaust gas recirculation system (EGR) 73 may be coupled to exhaustpassage 48 downstream of reformer 97. The EGR system may include an EGRvalve 74 and an EGR cooler 75 disposed along the EGR conduit 76. Fuelreformer 97 may assist in cooling exhaust gas recirculated to the enginevia EGR system 73.

An emission control device 70 is coupled to the exhaust passagedownstream of reformer 97. In some examples, emission control device 70may be located upstream of reformer 97. Emission control device 70 caninclude multiple catalyst bricks, in one example. In another example,multiple emission control devices, each with multiple bricks, can beused. In some examples, emission control device 70 may be a three-waytype catalyst. In other examples, example emission control device 70 mayinclude one or a plurality of a diesel oxidation catalyst (DOC),selective catalytic reduction catalyst (SCR), and a diesel particulatefilter (DPF). After passing through emission control device 70, exhaustgas is directed to a tailpipe 77.

Controller 12 is shown in FIG. 1 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, read-onlymemory 106, random access memory 108, keep alive memory 110, and aconventional data bus. Controller 12 is shown receiving various signalsfrom sensors coupled to engine 10, in addition to those signalspreviously discussed, including: engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling sleeve 114; a position sensor134 coupled to an accelerator pedal 130 for sensing force applied byfoot 132; a measurement of engine manifold pressure (MAP) from pressuresensor 122 coupled to intake manifold 44; an engine position sensor froma Hall effect sensor 118 sensing crankshaft 40 position; a measurementof fuel reformer tank pressure from pressure sensor 85; a measurement offuel reformer tank temperature from temperature sensor 87; a measurementof air mass entering the engine from sensor 120; and a measurement ofthrottle position from sensor 58. Barometric pressure may also be sensed(sensor not shown) for processing by controller 12. In some examples,engine position sensor 118 produces a predetermined number of equallyspaced pulses every revolution of the crankshaft from which engine speed(RPM) can be determined.

In some examples, the engine may be coupled to an electric motor/batterysystem in a hybrid vehicle. The hybrid vehicle may have a parallelconfiguration, series configuration, or variation or combinationsthereof.

Though FIG. 1 shows only one cylinder of a multi-cylinder engine, eachcylinder may similarly include its own set of intake/exhaust valves,fuel injector, spark plug, etc. Additionally, though FIG. 1 shows anormally aspirated engine, engine 10 may be turbocharged in someexamples.

Turning now to FIG. 2, an example method 200 for selectively storingreformate output by a fuel reformer is shown.

At 202, method 200 includes determining whether a fuel reformer is inoperation. For example, a fuel including an amount of alcohol, e.g.,ethanol, may be injected into the reformer. The reformer may reform thefuel into a gaseous reformate. For example, an ethanol reformer mayreform ethanol into a reformate gas comprising H₂, CO, and CH₄. Use ofgaseous reformate in an engine may assist in engine cold starts andengine knock reduction, e.g., during high load engine operatingconditions.

As described above, in some examples, the fuel reformer system mayinclude a water-gas shift catalyst to convert CO output by the reformerinto CO₂ and H₂. For example, the catalyst in the fuel reformer, e.g.,catalyst 72, may assist in a water-gas shift reaction to convert CO intoCO₂ and H₂. In other examples, a water-gas shift catalyst may bedisposed in a reformate fuel line, e.g., fuel line 69, in order toassist in a water-gas shift reaction. In this way, CO output by thereformer reaction may substantially be converted to CO₂ and H₂. However,even if a water gas shift catalyst is employed, CO may still be in thereformer output.

Thus, reformate output by the reformer may be directed through a CO trapdisposed in a reformate fuel line, e.g., CO trap 31. The CO trap mayseparate CO from other components in the reformate gas output by thereformer.

If the reformer is in operation at 202, method 200 proceeds to 206. At206, method 200 includes separating CO from the reformer output. CO maybe separated from the reformer output by a variety of methods and systemcomponents.

In some examples, the CO trap may include one or more molecular sievesto separate CO as reformate gas passes through the sieves. For example,a molecular sieve in the CO trap may include aluminosilicate minerals,zeolites, or synthetic compounds that have open structures through whichCH₄ and H₂ can substantially diffuse but through which CO will notsubstantially diffuse. Operation of a molecular sieve may depend onpressure and/or temperature of the CO trap. For example, an amount of COseparated by a molecular sieve may increase as a pressure of the CO trapincreases. Likewise, an amount of CO separated by a molecular sieve mayincrease as a temperature of the CO trap decreases.

In some examples, the CO trap may employ pressure swing adsorption toseparate CO from the reformer output. In pressure swing adsorption aplurality of adsorbent vessels may be included in the CO trap. Theadsorbent vessels may include adsorbent materials, e.g., aluminosilicateminerals and/or zeolites. By cycling pressure and/or temperature of theadsorbent vessels in the CO trap, near-continuous separation of CO fromthe reformate output may be achieved.

However, a delay may occur in output of CO by the CO trap, where thedelay may be a duration in which a first adsorbent vessel in a CO trapbecomes saturated with CO, e.g., when pressure swing adsorption isemployed. When pressure swing adsorption is employed, once the initialdelay has passed, then near continuous output of CO by the CO trap maybe achieved.

Before passing through the molecular sieve, reformate output by thereformer may comprise CO and non-CO gaseous components, e.g., H₂ andCH₄. The non-CO components may substantially diffuse through the sievematerial whereas CO may not substantially diffuse through the sievematerial. Thus, in some examples, when a molecular sieve is employed inthe CO trap, CO may be output by the CO trap during conditions whenreformate gas is not injected into the CO trap.

For example the pressure and/or temperature of the CO trap may increaseas reformate gas is injected into the CO trap (since non-CO componentsmay substantially diffuse through the sieve material but CO maysubstantially not diffuse through the sieve material). Thus, in someexamples, injection of reformate gas into the CO trap may be temporarilystopped so that CO may be purged from the CO trap and delivered to theengine and/or exhaust. For example, injection of reformate gas into theCO trap may be temporarily stopped when a pressure of the gas in the COtrap reaches a predetermined threshold value. In some examples, a valvemay be disposed in line 69 or in CO trap to control flow of reformateentering CO trap. In other examples, the reformer may be temporarilydeactivate during these CO trap purge cycles. The pressure of the gasesin the CO trap may be sufficient to drive delivery of CO to the engineor exhaust, e.g., via valve 43.

If pressure swing adsorption is employed in the CO trap, then aplurality of adsorbent vessels may be included in the CO trap andpressure cycles may be employed to continuously store and purge CO inthe adsorbent vessels. For example, once a first adsorbent vesselbecomes saturated with CO, reformate is diverted to a second adsorbentvessel in the CO trap while the first adsorbent vessel is purged of CO.In this way, near continuous output of CO by the CO trap may beachieved.

At 208, method 200 includes delivering separated CO to the engine. Forexample, valve 43 may direct CO output by the CO trap 31 to the intakemanifold 44 via fuel line 33 and injector 35. The CO output by the COtrap may be continuously fed into the engine at the rate at which itleaves the CO trap.

At 210, method 200 includes adjusting engine operating parameters basedon the amount of CO delivered to the engine. In some examples, theamount of CO delivered to the engine may be monitored via a sensor,e.g., a pressure or flow rate sensor, disposed in the CO trap or CO fuelline, e.g., fuel line 33. Engine operating parameters adjusted inresponse to injecting an amount of CO into the engine may include: sparktiming, cylinder air charge, amount of non-CO fuel injected in theengine, etc.

For example, an increase in the amount of CO injected into the enginemay result in an increase in at least one of spark timing and aircharge. For example, actuators such as the throttle, valve timing (e.g.,camshaft position), valve lift, and boost pressure may be set topositions that increase cylinder air charge when the amount of COinjected to the engine increases. Thus, the engine may be run lean whenCO is injected in the engine.

An increase in the amount of CO injected into the engine may also resultin a decrease in an amount of non-CO fuel injected to the engine, e.g.,from fuel tank 91 or reformate storage tank 93. For example, ifreformate is used to fuel the engine, e.g., during cold starts or highload conditions, and CO is output by the CO trap, the amount of non-COreformate delivered to the engine may be decreased. Likewise, if fuelfrom the fuel tank, e.g., tank 91, is used to fuel the engine, and CO isoutput by the CO trap, then the amount of non-CO fuel delivered to theengine may be decreased.

At 212, method 200 includes storing non-CO reformate output and/ordelivering non-CO reformate output to the engine. After the CO trapstrips the CO from the reformate gas output by the reformer, theresulting non-CO reformate may be delivered to the engine, e.g., toassist in cold starts or suppress engine knock during high loadconditions or stored for subsequent use by the engine. FIG. 3 shows anexample method 300 for delivering non-CO reformate output to the engineand storing non-CO reformate, e.g., in reformate storage tank 93.

At 302 method 300 includes determining if non-CO reformate is output bythe CO trap. Non-CO reformate may be output by the CO trap when the fuelreformer is in operation and the CO trap adsorbed the CO in thereformate output by the reformer, as described above. If non-COreformate is output by the CO trap at 302, method 300 proceeds to 304.In some examples, one or more sensors, e.g., a flow rate sensor, may bedisposed in the CO trap to determine an amount, e.g., a flow rate, ofnon-CO reformate output by the CO trap.

At 304, method 300 includes determining whether engine operatingconditions are met to deliver non-CO reformate to the engine. Incontrast to the continuous delivery of separated CO to the engine,non-CO reformate delivery to the engine may depend on a variety ofengine operating parameters. For example, non-CO reformate delivery tothe engine may occur during cold start conditions, when the temperatureof the engine is below a threshold temperature, or during high loadconditions, e.g., engine RPM above a threshold value, to reduce engineknock.

If engine operating conditions to deliver non-CO reformate to the engineare not met at 304, method 300 proceeds to 306. At 306, method 300includes determining if the amount of stored non-CO reformate is greaterthan a threshold value. In some examples, non-CO reformate componentsmay be stored in a quantity less than a threshold value, e.g., less than0.1 gasoline gallon equivalent (GGE), in order to decrease an amount ofgas leakage and increase safety in storing the gases. The amount ofnon-CO reformate stored may be determined by a variety of sensorsdisposed in a reformate storage tank. For example, a pressure and/ortemperature sensor disposed in a reformate storage tank may be used todetermine an amount of stored non-CO reformate.

If the amount of stored non-CO reformate is less than a threshold valueat 306, method 300 proceeds to 308. At 308, non-CO reformate output bythe CO trap is stored, e.g., in reformate storage tank 93.

However, in some examples, if the amount of stored non-CO reformate isgreater than a threshold value at 306, then method 300 proceeds to 310to deliver the non-CO reformate to the engine. In this case, thereformate storage tank may be filled to the threshold value, thus toprevent leakage conditions, the non-CO reformate may be injected to theengine at 310.

Following injection of non-CO reformate delivery to the engine at 310,method 300 proceeds to 312. At 312, method 300 includes adjusting engineoperating parameters based on the amount of non-CO reformate deliveredto the engine. In some examples, the amount of CO delivered to theengine may be monitored via a sensor, e.g., a pressure or flow ratesensor, disposed in the CO trap or CO fuel line, e.g., fuel line 33.Engine operating parameters adjusted in response to injecting an amountof CO into the engine may include, spark timing, cylinder air charge,non-CO fuel injection amount, etc.

For example, an increase in the amount of CO injected into the enginemay result in an increase in at least one or spark timing and aircharge. For example, actuators such as the throttle, valve timing (e.g.,camshaft position), valve lift, and boost pressure may be set topositions that increase cylinder air charge when the amount of reformateinjected to the engine increases.

However, if at 304 engine operating conditions to deliver non-COreformate to the engine are met, method 300 proceeds to 310. At 310,method 300 includes delivering non-CO reformate to the engine. In thiscase, non-CO reformate may be delivered to the engine to assist in coldstarts or to suppress knock, e.g., during high load conditions.

Following injection of non-CO reformate delivery to the engine at 310,method 300 proceeds to 312. At 312, method 300 includes adjusting engineoperating parameters based on the amount of non-CO reformate deliveredto the engine as described above.

Thus non-CO reformate storage or delivery to the engine may be based ona variety of engine operating parameters in contrast to the delivery ofCO to the engine which is continuously delivered to the engine at therate it is output by the CO trap. Since, CO is removed from thereformate before storage, reformate components produced by the fuelreformer, e.g., H₂ and CH₄, may be safely stored for use by the engine.

Continuing with method 200 in FIG. 2, following non-CO storage and/ordelivery to the engine, method 200 proceeds to 214. At 214, method 200includes determining if the reformer is deactivated. For example, engineoperating conditions may be such that the reformer reaction is stopped,e.g., if the temperature of the reformer is too low, if there isinsufficient alcohol in the fuel supplied to the reformer, or if one ormore components of the reformer system become degraded. As anotherexample, the reformer may be deactivated during an engine shutdown.

If the reformer is not deactivated at 214, method 200 returns to step206 to continue separating CO from the reformer output and combust it inthe engine and/or exhaust until the reformer is deactivated to stopproducing reformate.

If the reformer is deactivated at 214, method 200 proceeds to 218. At218, method 200 includes determining if the engine is running followinga deactivation of the fuel reformer. For example, engine operatingconditions may be such that the reformer reaction is stopped, e.g., ifthe temperature of the reformer is too low, if there is insufficientalcohol in the fuel supplied to the reformer, or if one or morecomponents of the reformer system become degraded. As another example,the reformer may be deactivated during an engine shutdown.

When the fuel reformer is deactivated, an amount of CO may remain in theCO trap following the deactivation. For example, CO may remain in theadsorbent material in the CO trap following deactivation of the reformerwhen reformate is no longer being produced. In some examples, the CO inthe CO trap may be purged following deactivation of the reformer.

If the engine is still running following deactivation of the reformer,then method 200 proceeds to 220. At 220, method 200 includes purging theseparated CO from the CO trap and delivering the purged CO to theengine.

Purging the CO from the CO trap may include adjusting one or moreoperating parameters of the CO trap. For example, a pressure of one ormore adsorbent vessels in the CO trap may be reduced to purge the COfrom the CO trap. Pressure may be decreased in one or more adsorbentvessels in the CO trap by adjusting one or more valves in the CO trap.For example, valve 43 may be opened while valve 47 is closed so that COis purged from the CO trap and delivered to the engine. In someexamples, purging the CO from the CO trap may include flushing the COfrom the CO trap using a gas. For example, exhaust gas or air may bedirected to flow through the adsorbent materials in the CO trap in orderto purge the CO from the CO trap.

As another example, a temperature of one or more adsorbent vessels inthe CO trap may be increased to purge the CO from the CO trap. In someexamples, temperature of one or more adsorbent vessels in the CO trapmay be increased by a heater located within the CO trap. In otherexamples, exhaust gas may be directed to flow through the CO trap inorder to increase the temperature to purge the CO from the CO trap.

At 222, method 200 includes adjusting engine operating parameters inresponse to the amount of CO purged. In some examples, the amount of COdelivered to the engine may be monitored via a sensor, e.g., a pressureor flow rate sensor, disposed in the CO trap or CO fuel line, e.g., fuelline 33. Engine operating parameters adjusted in response to injectingan amount of CO into the engine may include, spark timing, cylinder aircharge, non-CO fuel injection amount, etc.

For example, an increase in the amount of CO injected into the enginemay result in an increase in at least one or spark timing and aircharge. For example, actuators such as the throttle, valve timing (e.g.,camshaft position), valve lift, and boost pressure may be set topositions that increase cylinder air charge when the amount of reformateinjected to the engine increases.

An increase in the amount of CO injected into the engine may also resultin a decrease in an amount of non-CO fuel injected to the engine, e.g.,from fuel tank 91 or reformate storage tank 93. For example, ifreformate is used to fuel the engine, e.g., during cold starts or highload conditions, and CO is output by the CO trap, the amount of non-COreformate delivered to the engine may be decreased. Likewise, if fuelfrom the fuel tank, e.g., tank 91, is used to fuel the engine, and CO isoutput by the CO trap, then the amount of non-CO fuel delivered to theengine may be decreased.

Adjusting engine operating parameters in response to the amount of COpurged may also include adjusting engine operating parameters inresponse to how the CO trap is purged. For example, if exhaust gas isused to increase the temperature of one or more adsorbent vessels in theCO trap, then the engine operating parameters may be adjusted toincrease exhaust gas temperature. For example, the engine may operate athigher RPM. As another example, if exhaust gas is used to flush the COfrom the CO trap during the purge, then engine operating parameters maybe adjusted to increase exhaust flow rate, e.g. engine RPM may betemporarily increased to assist in the purging.

However, if the reformer is deactivated at 216 or 214 and the engine isnot running at 218, then method 200 proceeds to 224. In this case thereformer is deactivated when the engine is shutdown. As described above,following reformer deactivation, CO may remain in the adsorbent materialof the CO trap.

Thus, at 224, method 200 includes purging the separated CO from the COtrap and delivering the CO to the exhaust.

Purging the CO from the CO trap at an engine shutdown may includeadjusting a variety of engine and/or exhaust operating conditions. Forexample, purging the CO from the CO trap at an engine shutdown mayinclude depressurizing the adsorbent vessels in the CO trap to releasethe CO in the adsorbent material. Depressurization of the adsorbentvessels in the CO trap may include adjusting one or more valves in theCO trap as described above. For example, valve 47 may be closed andvalve 43 opened to direct the purged CO to the engine exhaustImmediately following an engine shutdown, the exhaust may remainsufficiently heated to combust the purged CO from the CO trap, or toreact in an exhaust catalyst, e.g., catalyst 70.

An example method 400 for purging CO from the CO trap during an engineshutdown is shown in FIG. 4.

At 402, method 400 includes determining if an engine shutdown isinitiated. For example, an engine operator may initiate an engineshutdown. Initiation of an engine shutdown may be sent to an enginecontroller, e.g., controller 12, in some examples. If an engine shutdownis initiated at 402, method 400 proceeds to 404.

At 404, method 400 includes determining if CO is in the CO trap. CO mayremain in the CO trap following a deactivation of the fuel reformer, asdescribed above. In some examples, one or more sensors may be disposedin the CO trap to determine an amount of CO in the CO trap. In otherexamples, an amount of CO in the CO trap may be based on operatingconditions of the reformer. For example, an amount of CO in the CO trapmay be based on how long the fuel reformer was running before it wasdeactivated. Additionally, an amount of CO in the CO trap may be basedon a size or type of catalyst and/or the number of catalysts in the COtrap. If CO is determined to be in the CO trap at 404, then method 400proceeds to 406.

At 406, method 400 includes determining if exhaust conditions for a COpurge are met. In some examples, a temperature of the exhaust system maybe measured, e.g. via a temperature sensor, and compared with athreshold temperature. The threshold temperature may be a temperatureabove which Co injected into the exhaust will be sufficiently combustedto CO₂. In other examples, an oxygen content of the exhaust and/oremissions control catalyst, e.g., catalyst 70, may be measured andcompared with an oxygen content threshold value. The oxygen contentthreshold value may be an amount of oxygen above which an amount of COinjected into the exhaust will become substantially oxidized to CO2. Theoxygen content threshold value may depend on the amount of CO injectedinto the exhaust.

If exhaust conditions for a CO purge are not met at 406, then methodproceeds to 408. At 408, method 400 includes adjusting engine and/orexhaust operating conditions so that exhaust conditions for a CO purgeare met.

For example, if the exhaust and/or emission control catalyst, e.g.,catalyst 70, does not have sufficient stored oxygen in order to oxidizethe amount of CO in the CO trap after an engine shutdown is initiated,the engine may be run lean for a plurality of combustion cycles beforediscontinuing combustion in the engine. As another example, the enginethrottle and/or valve timing may be adjusted following an initiatedengine shutdown to increase fresh air pumped through the engine as theengine spins down to rest. In this way, when CO is purged from the COtrap, more CO may be oxidized in the exhaust resulting in reduced COemissions.

In other examples, if the temperature of the exhaust is below athreshold temperature at which CO injected into the exhaust will besufficiently combusted, purging CO from the CO trap may be delayed for aduration until the exhaust reaches a threshold temperature. In this way,when CO is purged from the CO trap, more CO may be combusted in theexhaust resulting in reduced CO emissions.

Once the exhaust conditions for a CO purge are met at 406 or engineand/or exhaust operating conditions are adjusted at 408, then method 400proceeds to 410.

At 410, method 400 includes purging the separated CO from the CO trapand delivering the CO to the exhaust. For example, purging the CO fromthe CO trap at an engine shutdown may include depressurizing themolecular sieves or adsorbent vessels in the CO trap to release the COin the adsorbent material. Depressurization of the molecular sieves oradsorbent vessels in the CO trap may include adjusting one or morevalves in the CO trap. For example, valve 47 may be closed and valve 43opened to direct the purged CO to the engine exhaust.

Additionally, a rate of purging may be adjusted based on various exhaustconditions. For example, as a temperature of the exhaust increases, therate of CO purged from CO trap may increase, e.g., via adjusting valve43. As another example, as an oxygen content of the exhaust increases,the rate of CO purged from CO trap may increase, e.g., via adjustingvalve 43.

In this way CO may be purged from the CO trap and substantially oxidizedto reduce CO emissions and reduce storage of CO onboard the engine.

In some examples, a portion of CO in the CO trap may be used to keep thereformer catalyst warm during and following an engine shutdown event.For example, a purge rate of the CO in the CO trap may be reduced inresponse to an engine shutdown event in order to keep the reformercatalyst warm for a duration following the engine shutdown event. Inthis way, the reformer catalyst may be heated for a subsequentoperation.

Note that the example systems and methods included herein can be usedwith various engine and/or vehicle system configurations. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various acts,operations, or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedacts or functions may be repeatedly performed depending on theparticular strategy being used. Further, the described acts maygraphically represent code to be programmed into the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and nonobvious combinationsand subcombinations of the various systems and configurations, and otherfeatures, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsubcombinations regarded as novel and nonobvious. These claims may referto “an” element or “a first” element or the equivalent thereof. Suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.Other combinations and subcombinations of the disclosed features,functions, elements, and/or properties may be claimed through amendmentof the present claims or through presentation of new claims in this or arelated application. Such claims, whether broader, narrower, equal, ordifferent in scope to the original claims, also are regarded as includedwithin the subject matter of the present disclosure.

1-22. (canceled)
 23. A method for operating an engine, comprising:reforming a fuel into a gaseous fuel comprising H₂, CO, and CH₄; andselectively storing at least one of H₂ and CH₄ to a greater extent thanCO, wherein selectively storing at least one of H₂ and CH₄ includesoperating said engine by injecting at least one of H₂ and CH₄ to acylinder of the engine in response to an available amount of at leastone of H₂ and CH₄, engine speed, and engine load, and storing an amountof at least one of H₂ and CH₄ not used by the engine.
 24. The method ofclaim 23, further comprising separating the CO from the gaseous fuel andinjecting the separated CO in a cylinder of the engine after it isseparated from the gaseous fuel without storing the CO.
 25. The methodof claim 24, further comprising adjusting one or more engine operatingconditions based on an amount of CO injected into the engine.
 26. Themethod of claim 24, wherein adjusting one or more engine operatingconditions based on an amount of CO injected into the engine includesincreasing at least one of spark timing and cylinder air charge inresponse to an increase in the amount of CO injected into the engine.27. The method of claim 24, wherein the CO is separated from the gaseousfuel by a molecular sieve.
 28. The method of claim 24, wherein the CO isseparated from the gaseous fuel by pressure swing adsorption.
 29. Themethod of claim 28, further comprising separating an amount of CO fromthe gaseous fuel and injecting the amount of CO in a cylinder of theengine continuously after it is separated and adjusting engine operatingparameters based on the amount of CO injected in the cylinder, anddelivering at least one of H₂ and CH₄ to the engine based on engineoperating conditions and an amount of H₂ and CH₄ stored.
 30. A methodfor operating an engine, comprising: reforming a fuel into a gaseousfuel comprising H₂, CO, and CH₄; and selectively storing at least one ofH₂ and CH₄ to a greater extent than CO selectively storing at least oneof H₂ and CH₄ includes in a first condition where an amount of stored H₂and CH₄ is less than a threshold storing at least one of H₂ and CH₄, andin a second condition where an amount of stored H₂ and CH₄ is greaterthan a threshold not storing H₂ or CH₄ and delivering at least one of H₂and CH₄ to the engine.
 31. A method for operating an engine with a fuelreformer, comprising: operating the reformer to reform a fuel into agaseous fuel comprising H₂, CO, and CH₄; separating the CO from thegaseous fuel; injecting the separated CO in a cylinder of the engineafter it is separated from the gaseous fuel, wherein the CO is separatedfrom the gaseous fuel by a molecular sieve.
 32. The method of claim 31,further comprising adjusting one or more engine operating conditionsbased on an amount of CO injected into the engine.
 33. The method ofclaim 31, wherein adjusting one or more engine operating conditionsbased on an amount of CO injected into the engine includes increasing atleast one of spark timing and cylinder air charge in response to anincrease in the amount of CO injected into the engine.
 34. The method ofclaim 31, further comprising injecting the separated CO into an exhaustof the engine when the fuel reformer is deactivated.
 35. The method ofclaim 34 further comprising running the engine lean in response toinjecting separated CO in the engine, and delivering the remaininggaseous fuel to the engine, where the amount delivered is adjustedresponse to engine knock.
 36. The method of claim 31, further comprisingusing at least a portion of Co in the CO trap to keep a catalyst in thefuel reformer warm for a duration following an engine shutdown.